In academia one does it as part of a resume builder. Even academia pays a bit for the trouble and they certainly pay postage to and from. I have received anywhere from $50 to 150 for an article and over $500 for a detailed book review. However, that is academia and even there it depends on what they want you to do as it pertains to the details of the review... most provide a list of questions and guidance but they do not intend one to be a copy editor. Remember, your time is worth something to you. While you are reviewing other people's stuff you are not writing and if you do not get mentioned (even with pay) as a reviewer, if you do not have a nice semi-contractual agreement then I would have to ask how doing such would advantage you.
Lastly, I would try to find out just how 'legit' the publishers are... never hurts to do a little bit of investigation...:)
I used to do it for a small publisher (legitimate and good) until life took over. At the time, I was reading 12 or so books a month, and had time to do other stuff. Now, when I seldom manage 3 books a month, reading manuscripts had to go. But it was really enjoyable and I found it helpful to me. I got free books from the publisher as payment, no money. It's quite time consuming and sometimes the manuscripts might not be to your taste.
I wouldn't go anywhere near it before you confirm it's a legitimate publisher and how it works. The automatic question that comes up for me is why are you getting the invites and who are they coming from? Maybe I'm just extremely anal, but I don't take just anyone's opinion for reviewing submissions, which isn't to say I wouldn't take yours seriously, it's just that based on the questions you're asking here it makes me a bit suspicious.
In academia and with legitimate publishers sometimes they distribut manuscripts to 'subject matter experts' or persons known in the field who can provide constructive comments and criticisms to a developing manuscript. Again, this is undertaken either for 'resume' development or payment. Moreover, some reviewers are asked to provide comments which are used in advertising the product... its done all the time, you know, you've seen jacket covers with reviewer comments. However, I would remain cautious and the other two respondants bring up excellent points... time (which is your time) and the question of legitimacy by those requesting your input.
Appreciate all of this and have been going slow. Much of this generated from the recent Bouchercon convention -- so am trying to make some wise decisions and thus am researching and investigating. In my day job, I'm a senor writer-editor, so that also sometimes generates things like receiving a 1,150 word manuscript in my mailbox with a sticky, "Please let me know what you think." I was never sure whether to charge, but at B'con, they auctioned off reviews for megabucks, like with Charlaine Harris and others. It was an eye-opener! One friend, also an editor, suggested offering to edit rather than review, said that pays more? The trick for me is finding the time, as Donna said above, to get my own writing out and the stuff I want to read, read... before having to juggle all this other stuff. And Sandra, there are two and they do seem legit. One is a new publishing house just starting up and creating a review board, the other is one of the publishers I was a ghostwriter for. The start-up folks were at Bouchercon. Anyway, deeply appreciate all the good advice and insights. Hope it might help others know how it works, too. Thank you!
If you're going to do it, I'd say: stick with the house where you were a ghost and don't commit to anything long-term.
And don't be shy about broaching the money issue. I'd ask flat-out "What does it pay?" before even discussing it.
On my website, I've started tracking instances of newspapers (major ones!) asking people to write for free. Please don't tell me that I'm going to have track major publishers expecting people to serve as unpaid editors.
Excellent points! And agree. Stay tuned, I'll find out more soon and will let folks know how it turns out. I was told that it will involve reviewing about four books a year. Several authors told me they started doing this and gained a lot from it before it got too busy and impossible to do it anymore, so that was heartening. I was honored to get asked.